The present invention relates generally to the interfacing of I/O terminals with a switching network and, more particularly, describes a data interface for synchronizing standard dumb I/O terminals with a digital PABX.
An analog PABX switches I/O terminals, which may be either digital data or analog voice between each other for the communication of information. Also, trunk lines are provided for the interconnection of one PABX to another. In order that a terminal may be incorporated into the PABX system, an interface is usually required. As an example, binary encoded data generated by a terminal may be transmitted over standard telephone lines by interfacing the terminal into a telephone by use of a modem. However, modems are usually relatively expensive or electronically complex.
Digital PABX (with digital transmission to telsets) usually have high speed, say 64,000 bits per second or higher, synchronous transmission to and from the telset. I/O terminals for the conversion of alphanumeric characters into a data stream of a standard asynchronous code (such as the ASCII code with RS 232C protocol) usually require the interface first to buffer the data and then synchronize the data stream to the internal clock of the PABX. Such an interface requires complex logic and individual adjustment or baud rate settings in the field.